Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

Abstract

Hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatrography display gas chromatograms with dramatically rising baselines or "humps" of coeluting compounds that are termed unresolved complex mixtures (UCMs). Because the constituents of UCMs are not ordinarily identified, a large amount of geochemical information is never explored. Gas chromatograms of saturated/unsaturated hydrocarbons extracted from Late Archean argillites and greywackes of the southern Abitibi Province of Ontario, Canada contain UCMs with different appearances or "topologies" relating to the intensity and retention time of the compounds comprising the UCMs. These topologies appear to have some level of stratigraphic organization, such that samples collected at any stratigraphic formation collectively are dominated by UCMs that either elute early-(within a window of C 15 -C 20 of n-alkanes), earlyto mid-(C 15 -C 30 of n-alkanes), or have a broad UCM that extends through the entire retention time of the sample (from C 15 -C 42 of n-alkanes). Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-MS) was used to resolve the constituents forming these various UCMs. Early-to mid-eluting UCMs are dominated by configurational isomers of alkyl-substituted and non substituted polycyclic compounds that contain up to six rings. Late eluting UCMs are composed of C 36 -C 40 mono-, bi-, and tricyclic archaeal isoprenoid diastereomers. Broad UCMs spanning the retention time of compound elution contain nearly the same compounds observed in the early-, mid-, and late retention time UCMs. Although the origin of the polycyclic compounds is unclear, the variations in the UCM topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized. Isomerization of these constituents may have resulted from hydrothermal alteration of organic matter.

Optimization of an analytical protocol for the extraction, fractionation and determination of aromatic and aliphatic hydrocarbons in sediments

“…Several methods for hydrocarbons extraction from sediment samples have been described, and the most frequently used are Soxhlet, [2][3][4][5] ultrasonic extraction 6,7 and mechanical shaking. [8][9][10] Other approaches have also been applied, such as accelerated solvent extraction (ASE), 11,12 supercritical fluid extraction (SFE) 13,14 and microwaveassisted extraction (MAE).…”

Common Occurrences of Authigenic Pyrite Crystals in Cretaceous Oil Sands as Consequence of Biodegradation Processes

“…The TICs show the presence of unresolved complex mixture (UCM) humps. This is a common characteristic of oils that have undergone biodegradation [31][32][33]7,19,2]. TIC fragmentograms of oils extracted from the studied oil sands showing progressive depletion of chromatographically resolved hydrocarbons (e.g.…”

Composition of Organic Compounds Adsorbed on PM10 in the Air Above Maribor

“…UCMs appear in the chromatogram as large humps of complex mixture containing many components which are difficult to separate due to the large number of co-eluting compounds. 23,24 It is evident from Figure 11 that the position of UCM in the chromatograms of silylated sample extract is different regarding the seasonal time. During the late spring and summer atmospheric photo oxidation of VOCs may lead to the formation of particulate matter, also called SOA.…”

“…Consequently classic UCM of branched and cyclic hydrocarbon compounds typical for fossil fuels and originating mostly from lubricating oils from vehicle engine exhausts predominate. 24,25 …”